High sensitivity fiber refractometer based on an optical microfiber coupler

An optical microfiber coupler-based refractive index sensor is proposed and experimentally demonstrated in this letter. A microfiber coupler with a minimum diameter of 2.5 μm and a uniform waist with a length of 2 mm is fabricated and used for sensing surrounding refractive index. Both theoretical and experimental results have shown that the spectral response of the proposed microfiber coupler is highly sensitive to the surrounding refractive index over the range from 1.3340 to 1.3800. An average sensitivity of 2723 nm/RIU over this entire refractive index range has been achieved experimentally. Furthermore, for the refractive index range from 1.3340 to 1.3515, this sensor has demonstrated high sensitivity of 4155 nm/RIU.